SMP stall on process creation

SMP stall on process creation

[Daniel Jacobowitz]

I've been using a dual G4/500 with the linuxppc_2_5 tree for a couple weeks
now, and having all sorts of strange problems.  While trying to debug one
(console corruption on select, and sometimes on boot), I discovered
something very interesting.

I ran, in zsh, this command:
% time (for i in {1..100}; do /bin/echo -n; done)

on several machines.  On an old 604e/200:
  0.52s user 1.25s system 100% cpu 1.759 total

On a dual-450 celeron system:
  0.15s user 0.18s system 62% cpu 0.530 system

But on the G4:
  0.07s user 6.24s system 100% cpu 6.302 total

This obviously slows shell scripts to a crawl - forking or execing is being
severely penalized.  I'm also a little startled by the 100% cpu - this is a
multiprocessor system, that loop should NOT have been throttling both
processors.

Does anyone have any ideas?  I'm going to go play with 2.2 SMP and 2.4 UP
for comparison.

Dan

/--------------------------------\  /--------------------------------\
|       Daniel Jacobowitz        |__|        SCS Class of 2002       |
|   Debian GNU/Linux Developer    __    Carnegie Mellon University   |
|         dan@debian.org         |  |       dmj+@andrew.cmu.edu      |
\--------------------------------/  \--------------------------------/

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Re: SMP stall on process creation

[Tony Mantler]

At 3:00 PM -0600 12/16/2000, Daniel Jacobowitz wrote:
>I've been using a dual G4/500 with the linuxppc_2_5 tree for a couple weeks
>now, and having all sorts of strange problems.  While trying to debug one
>(console corruption on select, and sometimes on boot), I discovered
>something very interesting.
>
>I ran, in zsh, this command:
>% time (for i in {1..100}; do /bin/echo -n; done)
>
>on several machines.  On an old 604e/200:
>  0.52s user 1.25s system 100% cpu 1.759 total
>
>On a dual-450 celeron system:
>  0.15s user 0.18s system 62% cpu 0.530 system
>
>But on the G4:
>  0.07s user 6.24s system 100% cpu 6.302 total
>
>This obviously slows shell scripts to a crawl - forking or execing is being
>severely penalized.  I'm also a little startled by the 100% cpu - this is a
>multiprocessor system, that loop should NOT have been throttling both
>processors.
>
>Does anyone have any ideas?  I'm going to go play with 2.2 SMP and 2.4 UP
>for comparison.
[...]

Just ran this on my 9600/200mp, 2.4.0-test11 (linux-pmac-devel, not
terribly current). time says:
 0.84s user 2.63s system 100% cpu 3.466 total

I bumped the count to 1000, and ran top to verify. Top said (roughly) 16%
user (zsh, top, X), 40% system, 44% nice (seti@home, niced 19), which is
about what it should say with only one CPU throttled.

Not as zippy as it could be, but definatley not hammering both CPUs.


Cheers - Tony 'Nicoya' Mantler :)


--
Tony "Nicoya" Mantler - Renaissance Nerd Extraordinaire - nicoya@apia.dhs.org
Winnipeg, Manitoba, Canada           --           http://nicoya.feline.pp.se/


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Re: SMP stall on process creation

[Daniel Jacobowitz]

On Sat, Dec 16, 2000 at 03:34:14PM -0600, Tony Mantler wrote:
> At 3:00 PM -0600 12/16/2000, Daniel Jacobowitz wrote:
> >I've been using a dual G4/500 with the linuxppc_2_5 tree for a couple weeks
> >now, and having all sorts of strange problems.  While trying to debug one
> >(console corruption on select, and sometimes on boot), I discovered
> >something very interesting.
> >
> >I ran, in zsh, this command:
> >% time (for i in {1..100}; do /bin/echo -n; done)
> >
> >on several machines.  On an old 604e/200:
> >  0.52s user 1.25s system 100% cpu 1.759 total

> Just ran this on my 9600/200mp, 2.4.0-test11 (linux-pmac-devel, not
> terribly current). time says:
>  0.84s user 2.63s system 100% cpu 3.466 total

That's kind of upsetting right there :)

If I can figure out how to do profiling I'll try to track this down.

Dan

/--------------------------------\  /--------------------------------\
|       Daniel Jacobowitz        |__|        SCS Class of 2002       |
|   Debian GNU/Linux Developer    __    Carnegie Mellon University   |
|         dan@debian.org         |  |       dmj+@andrew.cmu.edu      |
\--------------------------------/  \--------------------------------/

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Re: SMP stall on process creation

[Daniel Jacobowitz]

On Sat, Dec 16, 2000 at 04:00:04PM -0500, Daniel Jacobowitz wrote:
>
> I've been using a dual G4/500 with the linuxppc_2_5 tree for a couple weeks
> now, and having all sorts of strange problems.  While trying to debug one
> (console corruption on select, and sometimes on boot), I discovered
> something very interesting.

Which was VGA console stuff, by the way.  I'm trying to get a second
opinion from linux-fbdev before touching the code though.

> I ran, in zsh, this command:
> % time (for i in {1..100}; do /bin/echo -n; done)
>
> on several machines.  On an old 604e/200:
>   0.52s user 1.25s system 100% cpu 1.759 total
>
> On a dual-450 celeron system:
>   0.15s user 0.18s system 62% cpu 0.530 system
>
> But on the G4:
>   0.07s user 6.24s system 100% cpu 6.302 total

And with test13:
    0.16s user 0.53s system 101% cpu 0.681 total

Much better.  Whatever it was seems to have wandered away again.  Note
that we're still a solid thirty percent slower than x86 at this - I'll
try to work out why some other time.

Dan

/--------------------------------\  /--------------------------------\
|       Daniel Jacobowitz        |__|        SCS Class of 2002       |
|   Debian GNU/Linux Developer    __    Carnegie Mellon University   |
|         dan@debian.org         |  |       dmj+@andrew.cmu.edu      |
\--------------------------------/  \--------------------------------/

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